Can't remember seeing a dog at the end. Could it be the animal that played the role of Nigger?
As BEagle said earlier. Go to the last couple of minutes of the film. Gibson and Wallis are talking outside of SHQ(?) - look over Gibson's shoulder and about 200 yards distant a black dog can be seen running around on an open grass area.
As you say because films are usually shot out of sequence it is probably the dog they used to "play" Nigger just having a bit of exercise..... but then again....